Electrical computers and digital processing systems: multicomput – Computer network managing – Computer network access regulating
Reexamination Certificate
1999-01-13
2002-05-28
Rinehart, Mark H. (Department: 2152)
Electrical computers and digital processing systems: multicomput
Computer network managing
Computer network access regulating
C709S226000
Reexamination Certificate
active
06397251
ABSTRACT:
This invention concerns distribution of multimedia files by file servers over an arbitrary network for information transfer, like a wide area network (WAN), for example the Broadband-ISDN or the Internet, or like a local area network (LAN). It is related to all time critical files which are coded with a variable amount of data over time, for instance, video files like movies, audio presentations, or teleconference presentations. In particular, the invention is directed to video-on-demand (VOD) services, as being envisaged for interactive television where the transmission quality is to remain constant despite given fluctuations in the amount of coded data, and where a continuous play-back of a demanded video is provided.
Known video file servers in such an environment serve as providers to play back compressed digital videos to clients over a telecommunication network. Those clients, on their side, need special decoders to convert the digital video signal in a television signal. These decoders comprise further a decoder buffer, and are usually implemented in a so-called Set-Top-Box. The videos are transmitted as frames of a given time duration. Commonly a predetermined constant bitrate for data file transfer is provided in order to achieve a simple management of network resources (FIG.
2
). As the compression ratio and therefore the size of a compressed frame of a video depends on the respective scene content, a compressed video comprises inherently a variable bitrate. For these reasons, file servers delivering movies are confronted with the problem of an extreme time dependent variation of information amount which has to be transferred from the server to the user at a given time.
A conventional multimedia data server is disclosed in U.S. patent application Ser. No. 288525 filed on Aug. 10, 1994, by the present applicant. Thisxserver comprises a direct access storage device (DASD), a plurality of data buffers, each of said buffers corresponding to a respective time interval associated with a multimedia presentation, ahd a mass storage device for storing the multimedia presentation data. A data bus connects the mass storage with the plurality of data buffers, wherein a bus switch is provided being operated by a controller.
A Set-Top-Box for the receiving side of a multimedia communication system according to the prior art is disclosed in U.S. patent application Ser. No. 473315 filed on Jun. 7, 1995, which is also assigned to the present applicant. This device effectuates local reception and processing of multimedia programs received from a remote multimedia file server. The local Set-Top-Box control system includes a DASD adapted to buffer a predetermined number of compressed program segments received from a multimedia file server. In particular, that invention is directed to a novel formatting methodology which provides concurrent presentation and buffering of program segments received from the server for on-demand viewing of a selected multimedia program.
Further for the transmission of compressed video files over a digital telecommunication link, for instance one operating in the known Asynchronous Transfer Mode (ATM), two compression modes are currently considered: constant bitrate and variable bitrate. These modes are illustrated in
FIG. 2. A
respective approach to achieve a constant bitrate, is to use a special compression mechanism with a so-called “closed-loop control” in the encoder that adjusts the picture quality as a function of the encoder buffer fill level. The respective variable quantization in the compression process leads to a variable quality. The quality decreases in scenes with high image complexity or heavy motion. In contrast, a compression process with constant quantization, of course, avoids the problem of changing quality, but it produces a video file with variable bitrate over time which is difficult to manage in networks with respect to the bursty traffic due to the fluctuating rate as a function of the scene contents.
The pre-cited known techniques are published in Proceedings of the 4th Open Workshop on High Speed Networks, Brest (France), September 1994, by Marcel Graf, and entitled “Traffic Shaping of VBR Video in ATM Endsystems”, which particulary concerns a method of traffic shaping, which drastically reduces the burstiness of a video stream.
A typical scenario for use of a file server coupled to a WAN is that at connection set-up time the user negotiates with the respective network provider a traffic contract that specifies the traffic the user injects to the network and the so-called “Quality of Service” (QoS) the user gets from the network. On the user side a traffic shaping function shapes the outgoing traffic so as to comply with the contract by buffering the cells to be sent. Traffic shaping is a means to control the burstiness of the traffic, but the transmission of realtime data imposes further constraints on traffic shaping. The individual video frames must arrive on time at the receiver. To eliminate jitter introduced in the transmission process, the receiver buffers the incoming frames in a smoothing buffer before they are decoded. The traffic shaping function introduces additional jitter. These two types of jitter need to be eliminated.
In the above article by M. Graf the trade-off between reducing burstiness and generating additional jitter and smoothing delay is analyzed, too. The proposed solution is a fluid model for video transmission, which enables to determine the jitter and smoothing delay introduced by shaping, as well as the buffer capacity requirements at the sender side and the receiver side. Jitter smoothing is achieved by properly delaying the start of the video decoder, wherein buffer underflow must be avoided, i.e. the consumption instant of each frame must not be earlier than the arrival instant of the frame in the buffer. In the article it is shown that jitter smoothing introduces an additional delay equivalent to the maximum jitter appearing in the frame sequence. It is observed that for movies or music recordings the quality of transmission is much more important than the starting time of a respective presentation. The user is already accustomed to initial delays in this area due to the necessary operation steps when starting a video tape on a video assembly or recorded music on a tape recorder. Hereby an initial delay of up to about ten seconds can be tolerated.
A similar approach is disclosed in an conference article by Wu-Chi Feng and S. Sechrest in Proceedings of the SPIE-The International Society for Optical Engineering (1995) Vol. 2417, p. 234-242, and entitled “Smoothing and buffering for delivery of prerecorded compressed video”. The authors propose a method for smoothing and buffering digital video data for delivery of pre-recorded compressed videos. The article is also concerned with the problem that transportation of compressed video data require the network to adapt to large fluctuations in bandwidth requirements if the quality of the video is to remain constant. The proposed use of a technique of averaging for smoothing video data allows for smoothing at the expense of a further source for delay.
A further prior art approach concerning multimedia video file distribution over WANs, given for example in U.S. Pat. No. 5,613,057, which is assigned to the present applicant. The invention described there—in contrast to the aforementioned approaches—intends to reduce the delay experienced by a user between the time of a presentation request and the presentation to the user, itself It is proposed to utilize two distributions sites, intermediate sites with which users interact and which combine limited storage facilities and fast communication channels for interacting with users. A main distribution site provides mass storage for files and slower and cheaper communication channels to the intermediate sites for the file distribution. The intermediate sites provide partial caching for some number of files. When a presentation request is received from a user at the intermediate site, the intermediate site det
Bracewell & Patterson LLP
International Business Machines - Corporation
Rinehart Mark H.
Vu Thong H
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